I'm concerned that there's rainwater slowly seeping through a small hole in my ceiling, beneath a flat roof. The hole is tucked away behind a boiler and it's difficult to know whether any water is actually coming through it. There was leakage before but the roof has recently been re-surfaced. Is there anything (lithmus paper perhaps?) that I can stick under the hole that would change colour or otherwise give a visual indicator if it got wet?
I know that there is such a test. You might try pilot shops, as they are used by some to detect water in fuel. I don't know if these particular ones would sense whilst totally "dry", if you see what I mean, though.
Christian.
Litmus is for acid v alkali. The traditional indicator for water, often used in silica gel drying packs, is anhydrous cobalt chloride (pink -> blue). You might also find that an old-fashioned scouring powder (such as Ajax) that has those blue dye specks in might help. When very dry they are almost invisible but given the slightest moisture they dissolve and colour the rest of the white powder blue.
But any chemical will eventually absorb moisture from the air. A cheap multimeter might work - set on the most sensitive resistance setting and compare your suspect patch with a known dry spot.
How about some of those silica crystals that come with electronic goods. Put them in the oven on a low heat to dry out. Then divide into two samples. One goes on a saucer near/under the hole. The other is a control placed at a similar height somewhere else in the room. Check and compare at daily intervals, and particularly after some rain.
Geoff
Yes, but how would you tell if your sample has absorbed water? They don't have a colour indicator. If you have a lab balance, that'd be one way.
A piece of coloured loo roll will give you enough colour change to find out if it's wet.
Try a sheet of white printer paper, or similar, or even some sheets of toilet paper laid flat near the hole - even if they dry out again you should be able to see wrinkles on the surface if theyve been wet at some time.
HTH
If there's a serious leak, they'll be swimming!
Yes, so would anything else - no need for silica gel.
Standard test for water - anhydrous cobalt chloride paper pink=dry blue=damp but water vapour in the air will produce the change, more common possibly anhydrous copper sulphate crystals - bake blue crystals in oven they turn white as water is expelled from the pentahydrate damp will change them blue again
nik
The stuff we have in work is a rather fetching blue colour when dry, and pink when wet, so there is silica gel available that can give you an indication
There certainly is - it's doped with cobalt chloride. But the little sachets which come with new equipment are not doped, and remain clear at all times.
I once (as a young Development Engineer over 40 years ago) had a similar conundrum with a fault on a particular B707 aircraft in the Weather Radar installation. I suspected water ingress at low altitude into the nose radome. I arranged (legally) for a piece of paper marked by an indelible pencil to be placed strategically within the radome. The paper obviously did get wet on some flights as evidenced by the marking turning purple and running. Simple, cheap and effective.
CRB
In message , BigWallop writes
Coloured crepe[1] paper (Xmas cracker hat) folded up in white bog roll works well for detecting leaks from plumbing.
[1] Or crap, I suppose.Cheers
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